This application is a 35 USC 371 application of PCT/DE 00/03387 filed on Sep. 28, 2000.
1. Field of the Invention
The invention relates to a method for producing a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a hollow base body which is equipped with a plurality of connection openings.
2. Description of the Prior Art
In common rail injection systems, a high-pressure pump, optionally with the aid of a prefeed pump, pumps the fuel that is to be injected out of a tank into the central high-pressure fuel reservoir, which is called a common rail. From the rail, fuel lines lead to the individual injectors, which are assigned one to each of the cylinders of the engine. The injectors are triggered individually by the engine electronics as a function of the engine operating parameters, in order to inject fuel into the engine combustion chamber.
One conventional common rail is described for instance in German Patent Disclosure DE 195 48 611. Conventional common rails are made from a forged blank, for instance. A longitudinal bore in the base body, the base body usually being elongated, acts as a fuel reservoir. The connection openings are created as a rule by bores. The region of intersection between the longitudinal bore and the connection bores, because of how it is produced, is sharp-edged and burred. Deburring and then cleaning the intersection region is complicated and expensive.
The object of the invention is to provide a method for producing a high-pressure fuel reservoir that is simple and economical. Furthermore, the high-pressure strength of the high-pressure fuel reservoir produced is to be improved.
In a method for producing a high-pressure fuel reservoir for a common rail fuel injection system of an internal combustion engine, having a hollow base body which is equipped with a plurality of connection openings, this object is attained in that a connection bore is predrilled, and that the communication between the connection bore and the interior of the base body is created with the aid of a further machining method. Within the context of the present invention, it has been found that the high-pressure strength of the high-pressure fuel reservoir, or common rail, is limited primarily by the intersections between the connection openings and the base body. By means of a machining step performed in addition to the drilling and deburring, the transitions between the connection openings and the base body can be blunted. As a result, the high-pressure strength of the common rail can be increased. In the present invention, the drilling is reduced to a predrilling operation. This markedly reduces drill wear. Moreover, the machining steps of drilling through and deburring are dispensed with.
A particular feature of the invention is characterized in that the further method involves an electrochemical machining method. With the electrochemical machining method, the communication between the predrilled connection bore and the interior of the base body is made on the one hand. On the other, a rounded transition between the predrilled connection bore and the interior of the base body is simultaneously created by the electrochemical machining method. This markedly increases the high-pressure strength of the high-pressure fuel reservoir according to the invention.
A further particular feature of the invention is characterized in that the connection bores are made at a tangent to the interior of the base body. For strength reasons, this arrangement of the connection bores has proved especially advantageous in practice. When the connection openings are being drilled through, however, drill breakage often occurs in this arrangement. This undesired tool wear is avoided by the two-staged creation of the connection bores that is provided for in the invention.
A further particular feature of the invention is characterized in that a plurality of connection bores are machined simultaneously with the aid of a multiple electrode. This reduces the machining time, which has a positive effect on production costs.
A further particular feature of the invention is characterized in that the intersection region between the connection bores and the base body interior is machined, in particular rounded, with the aid of the electrochemical machining. As a result, the intersection region can be optimized in a targeted way to improve the high-pressure strength of the high-pressure fuel reservoir of the invention still further.